The application of heat sensitive decalcomania (usually referred to simply as "decals") to selected substrata is well known. In particular, the use of reverse image sublimation type decals has grown in recent years, and it has become desirable to use such decals to place designs and photographs on solid objects. Devices heretofore utilized have been primarily, if not exclusively, for application of such decals to (a) planar objects, or (b) to objects which have non-planar surfaces primarily along a single axis, such as cylindrically shaped simple coffee cups.
However, in two important circumstances, the drawbacks of the existing devices known to us has become apparent. First, with respect to objects which are cylindrical, heretofore a separate device has been required to apply transfers to each unique radius of curvature. This is because such devices have been either built to substantially accommodate only one surface, or, have been built without sufficient provision for gas escapement in the pressure forming pad to allow escapement of all trapped gases as the device is secured against a curved surface. Second, most devices have been of the type wherein an object to which a decal is to be applied must be brought to the decal application device, rather than of the type where the device itself can be taken to a remote location for application of a decal to an object. Therefore, a continuing demand exists for a simple, inexpensive device which can be used to apply heat and pressure to heat sensitive decals in order to reliably transfer such decals to various curvelinear substrates.
Prior art devices of which we are aware and which suffer from one or more of the infirmities as described above are disclosed in U.S. Pat. No. 3,818,823 issued Jun, 25, 1974, to Bond for HEATED VACUUM PRESSURE PRESS; U.S Pat. No. 3,837,965 issued Sep. 24, 1974, to Mahon et al for PORTABLE REPAIR APPARATUS; U.S. Pat. No. 4,379,018 issued Apr. 5, 1983 to Griesdorn for HEAT TRANSFER APPARATUS; U.S. Pat. No. 4,874,454 issued Oct. 17, 1989 to Talalay et al. for DECAL TRANSFER DEVICE; and U.S. Pat. No. 5,019,193 issued May 28, 1991 to Aramini for ARRANGEMENT FOR AND METHOD OF APPLYING HEAT-TRANSFERRABLE DECALCOMANIA TO MUGS.
For the most part, the patent documents identified in the preceding paragraph disclose devices which are relatively fixed machines. Although the patent issued to Mahon superficially resembles the present invention, upon detailed examination it is clear that the Mahon et al vacuum pad/press lacks the interior structure which we have found advisable in order to form a wrinkle free bond on curved substrates.
Another common deficiency of the heretofore available heating pads for is the absence of a readily apparent visual indication to the operator of the progress and status of the decal application process, such as the time remaining until the decal application process is considered complete. The advantage of such an indication is important and self-evident.